Valvular heart disease is recognized as a common disease in the elderly population. Prevalence of valvular heart diseases increases indeed with age, from 0.7% in 18-44 year olds to 13.3% in the 75 years and older group (Nkomo, V T. et al., Burden of valvular heart disease: a population-based study, The Lancet, Volume 368, Issue 9540, Pages 1005-1011, 2006).
A mammalian heart valve comprises four heart valves which determine the pathway of blood flow through the heart. A mammalian heart generally comprises two atrioventricular valves namely the mitral valve and the tricuspid valve, which are located between the atria and the ventricles and prevent backflow of blood from the ventricles into the atria; and two semilunar valves (also known as arterioventricular valves) namely the aortic valve and the pulmonary valve, which are located in the arteries leaving the heart and prevent backflow of blood from the arteries into the ventricles.
The mitral valve, also known as the left atrioventricular valve, is composed of two valve leaflets (anterior and posterior), an annulus, a supporting chordae tendinae, and papillary muscles. The tricuspid valve, also known as the right atrioventricular valve, is made up of three valve leaflets (anterior, posterior and septal), an annulus, a supporting chordae tendinae, and papillary muscles. The aortic valve is composed of three valve leaflets (right, left and posterior) and an annulus. The pulmonary valve is made up of three valve leaflets (right, left and anterior) and an annulus. The fibrous aortic annulus, the fibromuscular pulmonary annulus and the muscular tricuspid and mitral annuli are linked to the leaflets. As the heart beats, the leaflets open and close to control the flow of blood. The leaflets of the atrioventricular valves are prevented from prolapsing into the atrium by action of the papillary muscles, connected to the leaflets via the chordae tendinae.
Mitral regurgitation—the mitral leaflets do not close properly leading to abnormal leaking of blood—is the most commonly occurring valve abnormality. In the US, in every age group, mitral regurgitation is the most common valvular disorder with a global prevalence of 1.7%, increasing to 10% in adults above 75 years old. (Nkomo, V T. et al., Burden of valvular heart disease: a population-based study, The Lancet, Volume 368, Issue 9540, Pages 1005-1011, 2006). Besides mitral regurgitation, conditions affecting the proper functioning of the mitral valve also include mitral valves stenosis -the opening of the mitral valve is narrowed leading to systolic function deterioration. Aortic valve, pulmonary valve and tricuspid valve may also be affected by regurgitation and stenosis. Heart valve regurgitation and stenosis have strong humanistic outcomes.
Typically, treatment for heart valve regurgitation or stenosis involves either administration of diuretics and/or vasodilators to reduce the amount of blood flowing back, or surgical procedures for either repair or replacement of the heart valve. Repair approach involves cinching or resecting portions of a dilated annulus, for example by implantation of annular rings which are generally secured to the annulus or surrounding tissue. Alternatively, more invasive procedure involves the replacement of the entire heart valve; mechanical heart valves or biological tissues are implanted into the heart in place of the native heart valve. These invasive procedures are performed either through large open thoracotomies or by percutaneous route.
However, in many repair and replacement procedures, the durability of the devices, or the improper sizing of annuloplasty rings or replacement heart valves, may result in additional issues for the patients. For this reason a significant part of patients with valvular heart diseases are denied for surgery. Indeed, despite guidelines for the management of patients with valvular heart disease, 49% of patients with severe mitral regurgitation, assessed by Doppler-echocardiography, are not referred to for surgery; mainly because of their advanced age, the presence of comorbidities, or impaired left ventricular ejection fraction (Mirabel, M. et al., What are the characteristics of patients with severe, symptomatic, mitral regurgitation who are denied surgery, European Heart Journal, Volume 28, Pages 1358-1365, 2007).
Less invasive approaches recently implemented involve pre-assembled, percutaneous expandable prosthetic heart valves. U.S. Pat. No. 5,840,081 discloses a method for implanting an aortic valve mounted on an expandable stent. However, human anatomical variability makes it difficult to design and size a prosthetic heart valve having the ability to conform to a heart annulus. Especially percutaneous atrioventricular valve replacement is a real challenge as the native atrioventricular valves annuli have a non-circular, non-planar, saddle-like geometry often lacking symmetry.